Cleansing Action of Detergent



The cleansing action of detergent and soap is fundamentally same.



When a detergent dissolves in water, its molecule will dissociate to form sodium or potassium ion and detergent ion ( detergent anion ).



The detergent ion such as R-O-

can be represented in a simplified

form by structure below.

O-



Hydrocarbon tail



Hydrophobic head



Ionic head



Dissolve in



Hydrophilic head

grease(dirt)



Dissolve in water

Cleansing action of detergents I.

Detergent molecule dissociate to form sodium or potassium ions and detergent ions.

II.

Hydrophilic region dissolve in water. Hydrophobic dissolve in grease and emulsifies the grease.

III.

When the water is shaken, the detergent ion will remove the dirt.

Cleansing Action of Soap and Detergent

Aim

: To compare and contrast the effectiveness of cleaning action of soap & detergent

Apparatus : 250cm3 beakers, 100cm3 measuring cylinder, glass rod Material

: Detergent & soap solution, soft water, hard water ( distilled water + MgSO4 ), pieces of cloth (2cm x 2cm) with oily stain

Procedures: 1. Prepare 4 beakers with the content below:

Experiment

Content

I II III IV

100cm3 of soap solution 50cm3 of soap solution + 50cm3 MgSO4 100cm3 of detergent solution 50cm3 of detergent solution + 50cm3 MgSO4

2. Stir the solution in each beaker using a glass rod until no changes can be observed 3. Record all changes that occurred 4. Place a piece of cloth with oily stain into each beaker. 5. Wash the oily stain on each piece using the solution in each beaker and stirred 6. Observe and record whether the oily stain on each piece of cloth dissapear.

Result:

Experiment

Observation

I

A lot of lather was formed. The oily stain was removed. The cloth was clean No lather but white precipitate was formed. The oily stain remained on the cloth. A lot of lather was formed. The oily stain was removed. The cloth was clean A lot of lather was formed. The oily stain was removed. The cloth was clean

II III

IV

Conclusion: Soap solution was an effective cleansing agent in soft water but not in hard water. Detergent solution was effective in both solution.

Cleansing Action of Soap and Detergent

1. Soap reduces the surface tension of water. 2. This increase the wetting ability of water. 3. So, the surface of cloth is wetted thoroughly

1. The hydrophobic part of the soap anion dissolves in the grease. 2. The hydrophilic part attracted to the water molecules.

1. Scrubbing helps pull the grease free from cloth surface.

1. Grease is removed from the cloth surface as tiny oil droplets. 2. Tiny oil droplets with negative charge repel each other. 3. This prevent them from redeposit on the surface.

CLEANSING ACTION OF DETERGENTS 

Synthetic detergents have the same type of molecular structure as soaps



i.e., one large non-polar hydrocarbon group that is water repelling (hydrophobic) and one short ionic group usually containing the or group that is water attracting (hydrophilic).



Thus the cleansing action is exactly similar to that of soaps whereby the formation of micelles followed by emulsification occurs.



However, synthetic detergents can lather well even in hard water.



This is because they are soluble sodium or potassium salts of sulphonic acid or alkyl hydrogen sulphate and similarly form soluble calcium or magnesium salts on reacting with the calcium ions or magnesium ions present in water.



This is a major advantage of the cleansing property of detergents over soap.